<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // 接口地址：https://api.apiopen.top/getJoke
        // p是一个Promise对象，resolve表示成功，reject表示失败
        const p = new Promise(function(resolve, reject) {

            const xhr = new XMLHttpRequest()
            xhr.open("GET", "https://api.apiopen.top/getJoke")
            xhr.send()
            xhr.onreadystatechange = function() {
                if(xhr.readyState === 4) {
                    if(xhr.status >= 200 && xhr.status < 300) {
                        // console.log(xhr.response);
                        resolve(xhr.response)
                    }else {
                        reject(xhr.status)
                    }
                }
            }
        });

        // value是成功的回调函数，reason是失败的回调函数
        p.then(function(value){
            console.log(value);
        }, function(reason) {
            console.log(reason);
        });

    </script> 
</body>
</html>